[roll third_party/pigweed] pw_thread: Fix small typo in docs

Original-Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/pigweed/+/171750

https://pigweed.googlesource.com/pigweed/pigweed
third_party/pigweed Rolled-Commits: 865e6cc5a9eabdf..cb408fd88b63404
Roller-URL: https://ci.chromium.org/b/8769516073377204945
GitWatcher: ignore
CQ-Do-Not-Cancel-Tryjobs: true
Change-Id: Ic952e785dc43e7bd4b740475b85ccae95364cec5
Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/experimental/+/171726
Bot-Commit: Pigweed Roller <pigweed-roller@pigweed-service-accounts.iam.gserviceaccount.com>
Commit-Queue: Pigweed Roller <pigweed-roller@pigweed-service-accounts.iam.gserviceaccount.com>
diff --git a/third_party/pigweed b/third_party/pigweed
index 865e6cc..cb408fd 160000
--- a/third_party/pigweed
+++ b/third_party/pigweed
@@ -1 +1 @@
-Subproject commit 865e6cc5a9eabdf166e36a86ffad8e8f2178320b
+Subproject commit cb408fd88b6340484f911fc7c26f6b3aa9816282